1. Field of the Invention
The present invention relates to a tag having an enclosed radio frequency identification (RFID) inlay and a method of making the same. More specifically, the present invention relates to an RFID inlay that includes an antenna having an integrally manufactured end portion which forms an electrical bridge over spiral turns of the antenna.
2. Background of Related Art
The use of a tag having an RFID inlay as part of an RFID system to identify and monitor objects is well known in the art. In particular, a reader of a conventional RFID system produces and emits an electromagnetic interrogation field at a specific frequency when excited by connected electronic drive circuitry. If a tag having an RFID inlay is positioned within the interrogation field for a sufficient time, the RFID inlay will become stimulated and transmit a uniquely coded signal that is received by the reader or a separate receiving antenna.
A typical RFID inlay includes an antenna and an integrated circuit (IC) chip connected to the antenna. One known antenna pattern of an RFID inlay is one that comprises of a plurality of turns that spiral around on a planar substrate (e.g., see U.S. Pat. No. 5,541,399xe2x80x94de Vall (1996)). A problem with this known pattern is that an electrical bridge must be formed over the spiral turns of the antenna in order for the two ends of the antenna to be electrically connected to an IC chip. This bridge is typically formed using one of the following methods: (1) using the IC chip as the bridge, or (2) connecting an additional (separate) electrical conductor to form the bridge. The IC chip or the additional electrical conductor forming the bridge is positioned on the same side of the substrate on which the antenna is mounted or on the opposite side. The IC chip is sometimes mounted on the additional electrical conductor forming the bridge.
In either of the two methods (1) or (2) noted above, the required manufacturing is relatively complex and costly. For example, if an additional electrical conductor is used to form the bridge, the conductor must be properly aligned and connected to on both of its ends.
Accordingly, there remains a need for an improved solution to this long-standing problem. The RFID antenna of the present invention fills this need by requiring a less costly and complex construction.
In an exemplary embodiment of the present invention, a radio frequency identification (RFID) tag (and a method of assembling the same) comprises a substrate, an integrated circuit, and a single, continuous antenna having a plurality of spiral turns and an end portion that is integral with the spiral turns. The spiral turns of the antenna are disposed on the substrate and the end portion crosses over at least one of the spiral turns. A non-conductive insulation may be arranged between the end portion and the at least one spiral turn that the end portion crosses. An electrical trace may be disposed on the substrate adjacent to an outermost spiral turn of the antenna. The end portion may be integrally connected to an innermost spiral turn and extend toward an outermost spiral turn to cross over substantially all of the spiral turns and connect to one end of the electrical trace. The other end of the electrical trace may be connected to the integrated circuit.
By forming the end portion as an integral part of a single, continuous antenna, the RFID tag can be manufactured at a reduced cost. A separate electrical bridge that crosses over spiral turns of the antenna does not have to be manufactured, cut, placed and electrically connected to the antenna. Since one side of the end portion is already integrally connected with the spiral turns, the number of electrical connections that need to be made are reduced. Furthermore, aligning an integral end portion as a bridge is easier than aligning a separately constructed bridge since it is already connected on one side.
In another exemplary embodiment of the present invention, a radio frequency identification (RFID) tag comprises a substrate, an integrated circuit and a continuous antenna including a plurality of spiral turns, a first end portion and a second end portion. The first and second end portions are integral with the spiral turns and the spiral turns of the antenna are disposed on the substrate. The first end portion crosses over at least a first one of the spiral turns, and a second end portion crosses over at least a second one of the plurality of spiral turns. The first end portion may be integrally connected to an innermost spiral turn of the antenna and extend toward an outermost spiral turn of the antenna. The second end portion may be integrally connected to an outermost spiral turn of the antenna and extend toward an innermost spiral turn of the antenna. In one further exemplary embodiment in which the end portions are folded over on the side of the substrate on which the spiral turns are disposed, non-conductive insulation is arranged between the first end portion and the at least a first one of the spiral turns and between the second end portion and the at least a second one of the spiral turns. Non-conductive insulation may also be arranged between the integrated circuit and at least some of the spiral turns. In another further exemplary embodiment, the first end portion crosses over the at least a first one of the spiral turns on the side of the substrate on which the spiral turns of the antenna are not disposed and the second end portion crosses over the at least a second one of the spiral turns on the side of the substrate on which the spiral turns of the antenna are not disposed. The integrated circuit is disposed on the side of the substrate on which the spiral turns of the antenna are not disposed and is connected to both the first and second end portions.